Lactic Dehydrogenase Virus (LDV) which infects mice permanently without overt clinical symptoms has profound and diverse effects on the murine immune system. During acute infection the virus has an adjuvant-like effect, prevents the development of tolerance with decreased cell-mediated immunity. We also have found that acute infection with the virus increases the susceptibility of mice to a murine plasmacytoma, MOPC-3l5. This is consistent with the histopathology of acute LDV infection which has revealed extensive destruction of thymus-dependent areas of lymph nodes and spleen. The effect of chronic infection with LDV has not been studied extensively. Chronic infection with LDV arrests the development of the autoimmune disease characteristic of (NZBXW) F1 mice. We have found that mice chronically infected with LDV are more resistant to plasmacytoma MOPC-3l5 and have proposed that chronic infection with LDV enhances cellular immunity. Preliminary evidence obtained in this laboratory indicates that persistent hyperglobulinemia is also associated with chronic infection. We intend to study the state of the lymphoreticular system in LDV-infected mice; specifically we intend to: a) study alterations in the levels and functional status of B and T lymphocytes during the course of viral infection, b) explore the mechanism(s) for T cell depletion and c) explore the effects of LDV infection in immunologically immature mice and in adult thymectomized animals. The studies proposed here should provide: a) a more rigorous appraisal of the perturbations resulting from infection by this virus in the populations of cells involved in the immune response, b) possible mechanism(s) responsible for these alterations, and c) some insight into the effects of the interaction of virus and the host immune system on its ability to establish persistent infection. BIBLIOGRAPHIC REFERENCES: Michaelides, Maria C., and Sondra Schlesinger; Effect of Acute or Chronic Infection with Lactic Dehydrogenase Virus (LDV) on the Susceptibility of Mice to Plasmacytoma MOPC-315; Journal of Immunology 112: 1560-1564 (1974). Michaelides, Maria C., and Herman N. Eisen; The Strange Cross-Reaction of Menadione (Vitamin K3) and 2,4-Dinitrophenyl Ligands with Myeloma Protein and Some Conventional Antibodies; Journal of Experimental Medicine 140: 687-702 (l974).